Barnsley defender Bambo Diaby has tested positive in a drug test reported to be done after the defeat against Blackburn on November 23.
Positive drug tests remain rare in football and cases take a long time to be processed, with a four-year ban the maximum punishment.
Despite being tested late in November, Diaby has still played for Barnsley with his last game coming against Huddersfield Town on January 11.
Former Southport defender Mike Phenix is believed to be the last positive case after testing positive for cocaine in September 2018 and his four-year ban was only announced in May 2019.
The Football Association works in partnership with UK Anti-Doping and drug testers regularly target players after games and at training grounds in out-of-competition tests.